24 Inquiry concerning the Nattire of Hcat> 



interrupted unnecessarily by description of instruments 

 in the midst of the accounts of interesting experiments, 

 I shall begin by describing the apparatus which was 

 provided for these researches ; and, as a perfect knowl- 

 edge of the instruments made use of is indispensably 

 necessary in order to form distinct ideas of the experi- 

 ments, I shall take the liberty to be very particular in 

 these descriptions. 



The thermometers, four in number, which were used 

 in these experiments, were constructed under my own 

 eye, and with the greatest possible care ; and, after 

 every trial I have been able to make with them, in 

 order to ascertain their accuracy, they appear to be very 

 perfect. 



They are mercurial thermometers, graduated accord- 

 ing to Fahrenheit ; their bulbs are cylindrical, 4 inches 

 long, and -j 4 ^- of an inch in diameter ; and their tubes 

 are from 15 to 16 inches long. The mercury with 

 which they are filled is quite pure, and they are freed 

 from air. Their scales were divided with the greatest 

 care; and, by means of a nonius, they show eighth 

 parts of a degree very distinctly; they are graduated 

 from about 10 degrees below the freezing point to 5 

 or 6 degrees above the point of boiling water. Their 

 bulbs are quite naked; their scales ending about i 

 inch above the junction of the bulb with its tube. The 

 freezing point is situated about 5 inches above the 

 upper end of the bulb. The reason for placing it so 

 high will be evident from the details of the experiments 

 in which these instruments were used. 



The instrument I contrived for ascertaining the 

 warmth of clothing is extremely simple ; it is merely a 

 hollow cylindrical vessel made of thin sheet brass. It 



